Laser photocoagulation therapy addresses ocular conditions such as retinal detachments and tears as well as proliferative retinopathy resulting from diseases such as diabetes. The abnormally high blood sugar in a diabetic stimulates the retinal vessels to release growth factors that in turn encourage an undesirable proliferation of blood vessels and capillaries over the retinal surface. These proliferated blood vessels are very delicate and will readily bleed into the vitreous. The body responds to the damaged vessels by producing scar tissue, which may then cause the retina to detach so as to eventually cause blindness.
In laser photocoagulation, a laser probe is used to cauterize the blood vessels at various laser burn spots across the retina. Because the laser will also damage the rods and cones that are present in the retina to allow vision, eyesight, as well as the blood vessels, is affected. Since vision is most acute at the central macula of the retina, the surgeon arranges the resulting laser burn spots in the peripheral areas of the retina. In this fashion, some peripheral vision is sacrificed to preserve central vision. During the procedure, the surgeon drives the probe with a non-burning aiming beam such that the retinal area to be photocoagulated is illuminated. Due to the availability of low-power red laser diodes, the aiming beam is generally a low-power red laser light. Once the surgeon has positioned the laser probe so as to illuminate a desired retinal spot, the surgeon activates the laser through a foot pedal or other means to then photocoagulate the illuminated area. Having burned a retinal spot, the surgeon repositions the probe to illuminate a new spot with the aiming light, activates the laser, repositions the probe, and so on until a suitable array of burned laser spots are distributed across the retina.
The number of required laser photocoagulations for any one treatment of the retina is large—for example, 1,000 to 1,500 spots are commonly burned. It may thus be readily appreciated that if the laser probe was a multi-spot probe enabling the burning of multiple spots at a time, the photocoagulation procedure would be faster (assuming the laser source power is sufficient). Accordingly, multi-spot laser probes have been developed and can be classified into two categories. A first category, denoted herein as a “multi-spot/multi-fiber” laser probe, produces its multiple laser beams through a corresponding array of optical fibers. A second category uses only a single fiber and is thus denoted herein as a “multi-spot/single-fiber” laser probe. Regardless of whether a laser probe is a single-fiber or multi-fiber probe, it should be compatible with the adapter used to connect the probes to the laser source. In that regard, it is conventional for a laser source to have a standardized interconnect such as a subminiature version A (SMA) interconnect. For example, the laser source may have a female SMA connector that receives a male SMA connector coupled to whatever instrument the laser source is driving. For a conventional single-spot/single-fiber laser probe, its male SMA connector will incorporate a single fiber. The laser source provides a focused beam known as the laser beam waist to the male SMA connector. This is quite advantageous for the single fiber probe since its optical fiber has its end face illuminated by the waist to enable efficient coupling to the laser source. But if a multi-spot/multi-fiber laser probe uses a corresponding plurality of fibers to drive its multiple spots, it cannot simply have its multiple fibers receive the focused beam from the source in this convenient single-fiber fashion because the laser waist is too narrow to couple into multiple fibers. Instead, the laser source would have to have its conventional interconnect changed or adapted so that the multiple fibers from the probe are not simply presented with the laser waist. But such changes are expensive and cumbersome.
Thus, a multi-spot/multi fiber probe has been developed such that the laser source drives a single fiber interconnect connected to a single fiber cable that in turn drives a single-fiber/multiple-fiber optical coupling within the laser probe handpiece. The resulting optics within the handpiece increase costs because it is desirable that the laser probe be disposable to limit contamination from patient to patient. For example, the optics include a diffractive beam splitter to split the beam from the single fiber into multiple beams for distribution to the multiple fibers. To collimate the laser beam from the single fiber onto the beam splitter and then condense the resulting multiple beams onto the multiple fibers requires plano-convex lenses. But it is very difficult to move such lenses to the laser source interconnect such that the remainder of the probe can be less expensive because of the relatively small inner diameter of such interconnects.
Another issue arises in multi-spot/multi-fiber laser probes in that the telecentric laser beams transmitted from the distal ends of the multiple fibers should be directed into different angular directions so as to properly distribute the resulting laser beam spots on the retina. To provide such distribution, a multi-spot/multi-fiber laser probe has been developed with the distal ends of the fibers bent into the desired angular directions. But such bending is cumbersome and increases costs as well.
To avoid the issues associated with the use of multiple fibers, the light beam from a single-fiber laser probe can be directed onto a diffractive beam splitter that splits the beam into multiple diffracted beams for transmission to the retina. However, the diffractive beam splitter must then focus the resulting diffracted beams, which requires the grating prescription to be spatially varying across the element. Not only does such a complication increase costs, the resulting spatially-varying diffractive beam splitter will reduce the overall performance. Such a design also makes varying the distance between the distal fiber end the diffractive element difficult.
Accordingly, there is a need in the art for improved multi-spot laser probes.